Full conversion in diastereoselective aldol additions using 'naked' enolates under catalytic amount of phosphazene base: The hydroxypinanone as chiral auxiliary

摘要

It was shown that a 'naked' enolate can undergo an aldol addition with full conversion provided that the Delta pKa between the aldol product and the conjugated acid of the base (which provides the necessary proton to the aldol-adduct) is large enough (>6 units). Under such conditions the base being regenerated can be used in catalytic amounts. When the iminoglycinate is derived from hydroxypinanone, 83% of the threo-isomer having similar to 98% ee (threonine) was obtained. [References: 11]